I have several questions and would wish me to help clarify. A. - It is true that, for a supercharged engine is beneficial to have some backpressure in the exhaust? I have a 2007 FX4 whipple supercharged, 5.4L, 3V, no cat, true dual X 2.5 ", I have no tailpipe emissions problems in my country, my problem is the power to the wheels. I install a high flow catalytic converters?. the Magnaflow 94106 is what many people recommend but in this forum, people from Bear Rivers says he does not meet the high flows, what is the correct part number, if anyone knows. 2. - have a 4.56 ratio 315/70R17 tires and power makes lose significantly?, is this true?. I have a big question, in particular point 1, because I think I lost torque at low rpm and, according to what I read, maybe this escape as free to be affecting the successful performance of the engine. Thanks.

 

Yes, you need some back-pressure otherwise you will lose power and performance.

Sorry, I do not know.

Forgive me (I know you said you are from another country), but I don't understand this last set of questions.

Stewart

 

1) Yes having back pressure does help with bottom end torque but it doesnt mean it gives better performance.

2) A quality aftermarket CAT will work but I would use a Magnaflow.

3) Yes switching to a shorter gear takes power away. Meaning if I go from a 3.55 to a 4:10 it will put down about 3-4% less power.

 

Actually, the manner in which I used the word, does mean it's better.

Since "performance" can be very subjective, unless it's used in relation to something very objective, like 1/4 mile ET's, depending on how it's used (very general term or very specific term) better performance can be had with proper back-pressure.

Throttle response and better lower end torque can all be described as performing better, compared to less throttle response and less torque.

I qualified the use of the word when I tied it to a loss of power.

Stewart

 

Less back pressure does mean less torque(it just might be moved up in the RPM band) but since his truck has a supercharger it wouldnt be that big of a deal and there wont be any lack of throttle response thanks to the supercharger.

By removing the cats he is removing back pressure and heat from the engine as well. This will cause a drop in boost and with less restriction it will allow the engine to live a longer and happier life with the stock pistons and rings.

If he wants his low end torque back then he needs to advance the stock cams and he can have the best of both worlds.

I qualified performance over a wide board.

 

Amen brother, yes you did!

Ummm, that means less torque, knucklehead!

Wait...did you mean "doesn't" (the way I read it) or did you mean "does?"

Maybe I'm the knucklehead!

Anyway, in this situation (and the one I had), less back-pressure equals less torque at the same RPM when compared to more back-pressure and more torque at the same RPM.

I'm not arguing peak torque (though I'm sure it's affected), and I'm not arguing torque isn't moved up in the RPM band, but what I said was correct. It makes less torque at a lower RPM when compared to the same RPM with the proper back-pressure.

Don't forget my friend, the cams in a truck are really very different than a car. The torque usually is brought on lower in the RPM band when compared to a passenger car.

Not true buddy.

One time when I had to smog my L, I had to pull my off-road (catless) pipes off and put my OEM catted pipes back on. I gained quite a bit more power when I re-introduced the back-pressure back on my truck, by putting the cats back on.

Not only did I gain power back in the lower end of the RPM band, but my throttle response (because the torque was back) was noticeably quicker. My truck was flat out faster with the cats on it.

And with less boost comes less power, if the SC is the same and hasn't been altered.

Stewart

 

I meant it does.

The cams in almost all the mod motors are the same. You would think otherwise but it is the case. I can give you a rough break down if you would like?

As I said, if he wants his low end torque he can use cam lockouts and manually adjust the cams to a 104-108 intake cam centerline (depending on PTV clearance). Most engines do not have the clearance to run tight as 104 though without using custom pistons(depending on lift of course)

Throttle response and torque are two completely different things. It's subjective but if I go WOT and nothing happens it can be lag from a turbo or a bad tune. Also if your truck isnt tuned for either setup then it will cause performance to suffer either way.

Have you forgotten physics?

By removing the cats he is reducing back pressure and reducing boost. Boost is just a measure of back pressure in the intake tract but the blower is still turning the same RPM and pushing the same CFM. He will drop 1-2 psi depending on the setup, but he wont be loosing any horsepower.

 

Yes, please do!

It was always my understanding the cams for the F150's were of a slightly different grind to produce torque lower in the RPM band.

Well duh brother. That's common knowledge...everybody knows that!



Yes, but I was just trying to relate my experience, and I did qualify my statement. I didn't mean to make a blanket statement connecting the two, if that's how you took it.

Yes...[start embarrassed smiley] I did, actually.

I got two different thoughts crossed in my head and made a faux pas. My bad.

Stewart

 

From my understanding the 2 valves have the same cams but have a longer runner intake manifold to produce that torque your speaking of. The 3 valves didnt need the change because of VCT.

I mainly do 4 valves of which I can give you a cam sheet so to speak on all of the Ford cams but it isnt related to the motor the OP has.

Right... Im sure you knew that. lol


So that means I won? lol I get double reps for that! rofl. j/k

 

Ok, I have been following with great interest the exchange of ideas in this post, very interesting, from there take the decision to buy a ULTRA FLOW X Dynomax 17553, reason, runs a high flow, less restrictive than the catalysts and the X to help balance the flows, but Iask, you already have an X, I answer, I will prove which is the result, which are the benefits, if any, on the other hand, the noise was too high, remember, I have installed free exhaust muffler with 2 single Borla Pro XS, then, I reduce the noise, I think some backpressure (when installed next week I will have a number) and I get that extra torque at low rpm. Now the big problem in my configuration are315/70R17 tires and 4.56 ratio, I think I must be losing about 40 RWHP, and this coincides with reality, should have about 400 RWHP and 360 RWHP I have. Whipple said that with the catalysts I will have more torque at low rpm but HP will continue the same, therefore , in my case, I lost about 2 psi of boost, but I had to increase the rpm of the supercharger, pulley OEM was 3.25 "and I had to make one of 2 7/8" to reach 7 to 8 psi of boost, 360 RWHP and have now, after installing this Dynomax muffler, a Mafia to control the values ​​of MAF, I go to a pulley 2.75 "to reach 10 psi of boost, telling me that the Dynomaxmuffler for uploading 1 psi of boost and the other to reach 10 psi psi of boost with the new pulley, these are all assumptions mine awaiting the outcome of the muffler.

 

A whipple supercharger doesn't care, it pumps air in with power from the motor. At low altitudes it will pump in the amount of air it is designed to max out at. Putting in higher ratio pulley will put out more air until you meet its designed max air flow. What you want is torque. You drive a slug. Torque to the ground thru a 4.11 or 4.56 is a must with large tires. Put in duals and high flow Catz and enough thought.